Go Back   Steve's Digicams Forums > Digital SLR and Interchangeable Lens Cameras > Pentax / Samsung dSLR, K Mount Mirrorless

Reply
 
Thread Tools Search this Thread
Old Dec 29, 2007, 4:29 AM   #1
Senior Member
 
Keithw's Avatar
 
Join Date: Mar 2007
Location: Oxfordshire, UK
Posts: 421
Default

I went for a walk in the Chilterns on Boxing Day and failed to take any photos that could be regarded as even half-decent. Walking back to the car I looked up and saw this plane:



So I swung the GX-10 striaght up and clicked. I had thought of asking whether we were on a main flight path or just a branch line but decided that that it wasn't as amusing as I hoped so didn't.

But when looking at he photo I got to wondering, and the more I wondered the more confused I got. The question is - why can I see the whole of the wing when ythere is a branch in the way?

A closer look at the plane:




shows the branch. Here is a 100% crop of the wing:



and while there is a bit of shadow where the branch is, I can still see the wing. Or can I? And if I can, why? Has the light bent around the branch? Or is that against the laws of physics? Is it just an optical illusion or is my brain playing tricks?

Too many questions and not enough answers. I'm confused!




Keithw is offline   Reply With Quote
Sponsored Links
Old Dec 29, 2007, 5:16 AM   #2
Senior Member
 
Alan T's Avatar
 
Join Date: Jun 2003
Location: Chester, UK
Posts: 2,980
Default

What was the shutter speed? It should be in the image files's exif data.

Here a guess, atentative theory:Maybe the twigs moved sufficiently to allow a mostly clear view of each bit of the plane in the time the shutter was open. The apparent movement of the plane is very, very small, but that of the twig, even if a very small distance, being very close to the lens, was a relatively large part of the field of view in those few milliseconds.
Alan T is offline   Reply With Quote
Old Dec 29, 2007, 10:38 AM   #3
Senior Member
 
NonEntity1's Avatar
 
Join Date: Jul 2006
Location: Lake Placid Florida USA
Posts: 2,689
Default

My guess would be that since the lens is wider than the branch it gathered light "around" the branch. In other words, the top of the lens could "see" some of the wing and the bottom of the lens could "see" the other portion of the wing. Since you werefocusing on the plane the branch is blurred out and you can see through it.

Tim
NonEntity1 is offline   Reply With Quote
Old Dec 29, 2007, 12:51 PM   #4
Senior Member
 
bilybianca's Avatar
 
Join Date: Nov 2005
Location: Hassleholm, Sweden
Posts: 3,435
Default

Tim is right, or nearly. The top of the lens, and the bottom of the lens, gathered the light that was behind the branch as seen from the middle of the lens. It's just a question of "front bokeh", out of focus blurring in front of the focus plane. (The focus plane is where the airplane is!:-))

You can use it to blur out a fence at the zoo if there is a long enough distance between the fence and the subject, and if you hold your camera near enough to the fence.The larger aperture you use, the less you see of the fence (or as in this case the branches).

Kjell
bilybianca is offline   Reply With Quote
Old Dec 30, 2007, 7:24 AM   #5
Senior Member
 
Keithw's Avatar
 
Join Date: Mar 2007
Location: Oxfordshire, UK
Posts: 421
Default

Thanks guys.

I think I understand what you are saying although if I think about it too much my brain begins to bleed :G

Happy new year folks!


Keithw is offline   Reply With Quote
Old Dec 30, 2007, 8:46 AM   #6
Senior Member
 
Alan T's Avatar
 
Join Date: Jun 2003
Location: Chester, UK
Posts: 2,980
Default

Keithw wrote:
Quote:
....I think about it too much my brain begins to bleed
Nonentity1 and billybianca are right & I'm wrong. It's not that hard if I can understand it.

Just draw a diagram of a lens, a distant object & a near object covering just part of the lens and you'll be able to see that from each point of the distant object you can draw rays in straight lines to the lens that miss the near object altogether, hit the lens, and are bent to hit the right point on the sensor. All these will form an image of that point of the distant object, slightly dimmed because a little less light got there, some of it having hit the twig. The twig is out of focus, just as they say, smudged in the extreme.

You can tell I'm just a stupid chemist and not a physicist. Though I've had to explain lots of chemistry to physicists in my time!

Fine piece of experimental observation by the way! Have you considered a career in science? Oh, no, scientist folk like me aren't needed any more; it's financial instruments and trading that are going to save the world, aren't they?

Alan T is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 4:15 AM.